mail19.mailserver-od.com has no NS records.
NS records for this zone are defined at mailserver-od.com.
NS records for this zone are defined at mailserver-od.com.
Question and response
Question
dig mail19.mailserver-od.com. NS
Answer
The response has no answer records.
Authority
mailserver-od.com. 900 SOA ns-1485.awsdns-57.org. dnsadmin.socketlabs.com. 2017021500 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0